Humbucking arrangement for magnetic transducers



Sept. 27, 1949. c. w. CLAPP 2,483,123

HUMBUCKING ARRANGEMENT FOR MAGNETIC TRANSDUCERS Filed Nov; 2, 1944 Inventor: Charles W. Clapp,

His Attorney.

Patented Sept. 27, 1949 ICE HUMBUCK NG ARRANGEMENT FOR MAGNETIC TRANSDUCERS Charles W- G m Albany, N. Y., assignor to Gen eral Electric Company, a corporation of New York Application November 2, 19514, Serial No. 581,559 Claims. (01. 179-100,2)

My invention relates to improveme ts in magnetic recording and reproducin head ior use in connection with magnetic recordin evices in which voice or other signals are recorded and ultimately reproduced, if desired, with a r cording medium in the nature of an elon ated. ma netic member, such as a wire, tape, or thelilrs'ii Recording and IBDIQduOing heads currently use in connection with magnetic wire or tape recording apparatus have been .iound to be particularly sensitive to stray magnetic fields originating externally or the recording heads. 0pdinarily. a complete recording apparatus includes an alternating current motor for driving the Wire reels and a power transformer from which unidirectional current for the voice modulation circuits is derived througha rectifier. Both the motor and transformer ordinarily operate at a readily available low frequency, such as .60 cycles per second. It is not always possible, par icularly in portable apparatus, so to position or shield the power circuits that the stray magnetic fields arising therefrom have an inappreoiable efiect upon the recording and reproducing head. Su s ay fields, it not neutralized, caus uhdesirable hum reproduction.

It is also found that, a recording and reproducing head is so unbalanced magnetically.

that it is arrested Isl/" stray fields in reproducin it usually establishes undesired external fields when used for the recording operation. Such external fields es ablish d in the recor ing operation interfer with anyreproduc hg head op rating in close proximity thereto,

Ac ordingly, it a eneral object of my in vention t providenew a d improv d means f r ma n ical y balancin .a ma netic recordin and eproducing head.

It is a further ob ct of my inventi n to provi n w and imp oved means for preventing the establishment f p ciable external fi d y a magnetic recording head. i

It is another object of my inventio to ros vide a new and improved magnetic recording an eproducing he d which is substantially i sensitive to magnetic fieldsoriginating externally 0f the head,

It is a still further object of my inv nt on to provide means in rendering a magnetic recording and reprodu in h ad substantially inse s tive o stray magnetic fields originating outside he h ad, and more particularly to magnetic fields originating f om power circuits th recording apparatus, without reducing the sensitivity of the head to local fields associated with the ma netic recording medium pas ing therethrough.-

My nvention will h more fully unders ood and its bj ct and advantages further: app ciated by ref rin new to the .tollowingdetailed specifi ation taken in conjunction with the accompanyin drawing, in whichl ig. 1 is a diagrammati repres ntation of a ma netic wire recordi g and repr duc n apparatus; and Figs. 2-10. inclusive, are diagrammatic representat s of a plu al ty f recording and reprodu ing h ads em b dy n my invention in a variety of forms.

Refer-rin now to the drawin s, I have shown at Fi l a wire reeling and r cordin sy t m for a ma netic wire recording and reproducin appara us comprisin .a pair of rotatably m un d pools or Wire reels l and 2, a pair .of idler pulleys 3 and 4 positioned between the reels 1 and 2, and a suitable ma netic recordin m dium, su h as a wire 5, wound at opposite ends upon the reels l and 2 and passing over the pulleys 3 and i and through a magnetic recording and reproducing head .6 positioned between the idler pulleys. The idler pulleys 3 and 4 are rotatably mounted on fixed pivots thereby to preclude lateral movement of the wire where it passesthroug-h the head 6 as the wire is wound from one to the other of the reels l and 2. A suitable driving motor, not shown, is arranged for connection to either the reel 1 or the reel 2 so that the wire 5 may be Wound in either direction. it will :be understood that recording and reproduction are both carried out with the wire 5 traveling in the same direction, but it is necessary to run the wire backward between the two operations.

The recording and reproducing head 6 ordinarily comprises a substantially closed magnetic core ring havin a pair of confronting pole faces defining an air gap .therebetween and provided with a ma netizing'winding. traveling magnetic recording medium 5 traverses a path through the air gap, so that the wire acts as a shunt across the gap and m n tiz d as it passes throu h the head. signal modulated currents are supplied to the magnetizing winding, so that the magnetization .of the recording medium is varied along its length as the wire travels hrough the head. recording medium may be pa sed through or adiacent h qair p, and he wire is ma n tized either longitudinally or transversely depending upon its direction of t ave pas the gap.

At Fi 2, i have shown a preferred form of my invention in which the magnetic recording and ep oducing comprises a pair of similar conducting winding comprising a pair of similar coils l3 and I4 mounted in lateral spaced relation upon opposite sides of the magnetic core for 7 use in both recording and reproducing operation. Preferably, the axes of the coils I3 and I4 are substantially parallel to the plane of the air gaps 9 and II), as shown at Fig. 2. The coils l3 and I4, as shown, are oppositely wound and connected in series circuit relation, so that current traversing! the coils in recording operation sets up magnetic. fields in aiding relationin the two halves of the core. established in the magnetic core by the wire 5, which acts as a small magnet of varying strength bridging the gap 9, induces voltages in like phase relation inthe coils I3 and I4. It'will of course be understood by those skilled in the art that, if desired, the coils I3 and I4 may be connected in parallel circuit relation and disposed on the core in aiding relation to establish flux in thecore, whereby voltages induced in the coils by flux originating in thehead will also be of like polarity with respect to the external circuit.

It may nowbe noted that the magnetic core ring I, 8 of Fig. 2 provides two substantially parallel magnetic paths through'the core for stray flux originating externally of the recording head and having any direction in the plane of the core. It will be evident that for components of stray flux in the plane of the core having a direction substantially parallel to the plane of the airgaps 9 and II), the voltages induced-in the series connected coils I3 and I4 will be in opposite phase relation and nearly equal in intensity. Such approximate balance of induced voltages will be attained when the core sections 1 and 8 have similar shapes and substantially the same reluctance, and the coils I3 and I4 have substantially the same number of turns and are symmetrically positioned upon the core sections, as shown at Fig. 2. Similarly, if the coils are connected in parallel circuit relation, such stray flux, being in opposing relation in opposite halves of the core, will induce in the coils voltages opposite in polarity with respect to the external circuit.

The reluctance of the air gaps 9 and 19 has no appreciable efiect upon the intensity of voltages induced in the coils I3 and I4 by components of stray flux in a direction parallel to the axes of the coils. The induced voltages are, however, dependent upon both the reluctance of the core sections and the number of turns in the coils. If it is necessary to make any adjustment in order fully to balance the voltages induced in the coils, such adjustment may be made either by varying the reluctance of the core sections between the gaps, or varying the number. of turns on the coils. In practice, if the core sections 1 and 8 are integral between the air gaps 9 and I9, adjustment for flux parallel to the axes of the coils is preferably made by varying the number of turns upon one or the coils. With the induced voltages thus balanced by the symmetrical construction of the head, the net voltage appearing at the terminals of the entire winding including both coils I3 and Id will be substantially zero.

In the form of the invention shown at Fig. 2,

Conversely, in reproducing operation, flux components of stray flux originating externally of the recording head and in a direction perpendicular to the axes of the coils I3 and Ill in the plane of the core follow parallel paths through the air 5 gaps 9 and I0. Thus, the head may be balanced for components of stray flux in this direction by adjusting the reluctance .of one or both of the air gaps 9 and I0. It will be evident that, by proper adjustment of the reluctance of the air gaps, the stray flux flowing through opposite sides of the core in a direction perpendicular to the axes of the coils l3 and I4 may be so proportioned and distributed that equal and opposite voltages 1 are induced in adjacent halves of each of the coils 13 and I4. With such adjustment, the net induced voltage at the terminals of the winding in response to components of stray flux perpendicular to the coil axes and parallel to the plane of the core will be substantially zero.

Adjustment of the reluctance of the air gaps 9 and ID may be effected either by moving the core sections 1 and 8 relative to each other or by providing small magnetic shunts I5 attached to a pole piece on one side of each gap and bendable to provide the desired reluctance.

Components of stray flux in a direction perpendicular to the plane of the-magnetic core. I, 8 link no turns of the coils I3 and I4, and therefore induce no voltage in these coils. Thus, it will be evident that when properly balanced the magnetic recording head of Fig. 2.is insensitive to components of stray magnetic flux. originating externally oi the head along three mutually perpendicular axes, and is therefore. insensitive to stray magnetic fields in any direction in space. While my invention provides precise neutralization for homogeneous stray fields, it will be evident that efiective balancing in non-homogeneous fields is also possible. 40 At Fig. 3 I have shown another embodiment of my invention similar in'all respects to that shown at Fig. 2 except that the magnetic core sections 1 and 8 are shaped to provide 3, rectangular, rather than a circular, multi-section core. It will be understood, of course, that if desired one or both of the air gaps 9 and ll] of the head shown at Fig. 3 may be provided with magnetic shunts I5, as shown at Fig. 2. Balancing of the head of Fig. 3 is carried out in the same manner as described in connection with Fig. 2.

At Fig. 4 I have shown a still further embodiment of my invention in which a rectangular magnetic core is formed-of two dissimilar core sections I6 and I1 spaced apart to provide a pair of oppositely disposed air gaps 9 and I0 symmetrically disposed about an axis perpendicular to the plane of the gaps. In this form of the invention, the core section It forms three sides of the rectangular frame and the core section I! forms the fourth side.- With this arrangement, the core sections I6 and I! are obviously of different reluctance so that, in order to balance the voltages induced in the coils I3 and [4 by components of stray flux having a direction substantially parallel to the axes of the coils, it is necessary that the coil on the section of greater reluctance have more turns than the coil on the section of smaller reluctance. As in Fig. 2, the coils I3 and I4 of Fig. 4 are disposed on opposite legs of the core with their axes substantially parallel to the plane of the gaps 9 and III, so that balancing of the head for components of stray flux in the, plane of'the core and in a 75 direction substantially perpendicular to the axes or the coils may be effected by adjusting the reluctance of one or both the air gaps 9 and Ill. The head shown at Fig. 4, as well as all other embodiments of the invention herein described, is inherently insensitive to components of stray fiux perpendicular to the plane of the core.

- At Fig. I have shown an embodiment of the invention similar to that shown at Fig. 2 except that the magnetic core is formed in four sections i, la, 8 and So having an additional pair of air gaps I8 and I9 diametrically disposed and'intere mediate the gaps 9 and III. The gaps I8 and I9 may be used to control the reluctance of the parallel magnetic paths through the core between the gaps .9 and III for components of stray flux in a direction parallel to the axes of the coils I3 and I4. Thus, balancing for stray flux in this direction may be effected by adjusting the reluctance of the gaps I8 and I9, rather than by changing the number of turns on the coils I3 and I4, asdescribed in connection with Fig. 2.

At Fig. 6 I have shown an embodiment of my invention in which an annular magnetic core is formed of three similar sections 20, 2|, and 22 spaced apart to form a. main air gap 9 traversed by the magnetic Wire 5 and a pair of auxiliary air gaps 23 and 24. The winding comprises coils I3 and I 41 mounted upon the annular core in a manner similar to the coils I3 and I4 of Fig. 2.

If any one of the air gaps of the head shown at Fig. 6 is formed to provide a fixed reluctance, the head is adjusted for balance in the same manner as heretofore described in connection with Fig. 2. If, however, the three gaps 9, 23, and 24 of Fig. 6 are all adjustable in reluctance the head shown in this figure may be balanced for mutually perpendicular components of fiux in the plane of the core either by the method outlined in connection with Fig. 2, or by adjustment of gap reluctance alone without regard to the number of turns upon the coils I3 and I4. It will be understood, of course, that an approximate balance is first obtained by building the coils I3 and I4 with substantially the same number of turns. For precise adjustment by gap reluctance alone, the induced voltages are first balanced for components of stray flux parallel to the axes of the coils I3 and I4 by adjustment of the air gaps 23 and 24. Following this adjustment, the head is balanced for components of stray fiux in a direction perpendicular to the axes of the coils I3 and I 4 by adjustment of the reluctance of the air gap 9.

At Fig. '7 I have shown another embodiment of my invention similar to that shown at Fig. 6, except that the magnetic core is rectangular rather than annular, being formed of a pair of L-shaped sections 20a and 22a defining the main air gap 9 and a straight section 2Ia spaced from the L-shaped sections to define a pair of auxiliary air gaps 25 and 26. Balancing of the head shown at Fig. 7 is accomplished in a manner entirely similar to that described above in connection with the head shown at Fig. 6.

At Figs. 8, 9 and 10 I have shown embodiments of my invention similar in structure principle to the embodiment shown at Fig. 2, but in which the confronting pole pieces of the core defining the main air gap 9 are formed to accommodate for various directions of travel a magnetic recording medium in the form of a flat tape to. In each of these figures, the head is annular and formed of two semicircular sections providing diametrically disposed air gaps, as at Fig. 2. Fig. 8 shows the manner in which the flat tape 5a maytraverse the gap 9 .for longitudinal magnetization; Fig.9 shows the manner in which the tape 5a is accommodated in the gap 9 for transverse magnetization across its thickness; and Fig. 10' shows the .manner in which the tape 5a traverses the gap 9 for transverse magnetization across its width.

.While all the foregoing embodiments of my invention utilize :only: a single gap in the core for 'recordingor reproducing, itnwill be understood that if 'desired additional recording media may be passed through other of the gaps without departing from my invention.

:While Ifihavei shown only certain preferred embodimentsof; my invention by way of illustra tion, many other modifications will occur to those skilled in the art, and I, therefore, wish to have it" understood that .I intend in the appended claims to cover all suchmodifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent'of the United-States is: V

1. In a magnetic recording and reproducing head, a multi-section magnetic core comprising a plurality of sections in spaced relation defining a main air gap and a plurality of auxiliary air gaps symmetrically positioned about the axis of said main air gap, said sections adjacent said main air gap being formed to accommodate a traveling magnetic recording medium traversing said main gap, a divided winding including a pair of similar coils mounted upon said core on opposite sides of said main air gap with the axes of said coils in substantially parallel spaced relation, said coils being so proportioned and positioned that substantially equal and opposite voltages are induced therein by components of stray flux in a direction substantially parallel to the axes of said coils, and means for adjusting the reluctance of said auxiliary gaps so that substantially equal and opposite voltages are induced in each half of each said coil by components of stray flux substantially perpendicular to the axes of said coils in the lane of said core.

2. In a magnetic recording and reproducing head, a magnetic core comprising a pair of dissimilar core sections disposed with their pole ends in confronting spaced relation to define a pair of aligned oppositely disposed air gaps therebetween, said core having an axis of symmetry substantially perpendicular to the plane of said gaps, said sections adjacent one of said gaps being formed to accommodate a traveling magnetic recording medium traversing said one gap, a divided winding comprising a coil mounted upon each said section with the axes of said coils in substantially parallel spaced relation, said coils being so proportioned that substantially equal and opposite voltages are induced therein by components of stray flux in a direction substantially parallel to the plane of said gaps, and means for adjusting the reluctance of the other of said gaps to render substantially equal and opposite the voltages induced in each half of each said coil by components of stray flux in a direction substantially perpendicular to the axis of said gap in the plane of said core.

3. In a magnetic recording and reproducing head, a substantially closed magnetic core having a pair of confronting pole pieces defining an air gap therebetween, said pole pieces being formed to accommodate a traveling magnetic recording medium traversing said gap, a winding on said core, and means for balancing voltages induced in said winding by stray flux originating externally of said head comprising an adjustable magnetic shunt mounted upon at least one of said pole pieces adjacent said air gap. 7

4. In a magnetic recording and reproducing head, a substantially closed magnetic core having a pair of confronting pole pieces defining an air gap therebetween, a divided winding on said core comprising a pair of coils mounted upon opposite sides of said core and connected to neutralize voltages induced in said coils by components of stray flux in a direction substantially parallel to the axes of said coils, and means for balancing voltages induced in said coils by components of stray flux in other directions in the plane of said core comprising an adjustable magnetic shunt mounted upon at least one of said pole pieces adjacent said air gap.

5. In a magnetic recording and reproducing head, a multisection magnetic core comprising a plurality of sections in spaced relation defining a main air gap and at least one auxiliary air gap therebetween, a divided winding comprising a pair of. coilsmo'unted upon opposite sides of said core with their axes substantially parallel to the plane of said main air gap and connected in aiding relation to establish flux in said core, and an adjustable magnetic shunt mounted upon at least one of said polepieces and operable to vary the reluctance of the associated air gap thereby to balance, voltageslinduced in said coils by components of straywflux .in a direction substantially perpendicular to the axes of said coils in the plane-of said core. a

. CHARLES W. CLAPP.

REFERENCES CITED UNITED STATES BA'IENT Number Name Date 2,351,003 Camras June 13, 1944 2,351,004 Camras June 13, 1944 

